Podcast
Questions and Answers
What is the unit of measurement for clearance?
What is the unit of measurement for clearance?
- mg/L
- L/hr or ml/min (correct)
- mg/hr
- mg/mL
What determines the rate of elimination of a drug?
What determines the rate of elimination of a drug?
- The plasma concentration of the drug (correct)
- The patient's age
- The patient's weight
- The dose of the drug administered
What is the total body clearance (CL total) of a drug?
What is the total body clearance (CL total) of a drug?
- The sum of all clearances from the drug-eliminating organs
- The sum of all clearances from the drug-metabolizing and drug-eliminating organs (correct)
- The difference between the liver and kidney clearance
- The sum of all clearances from the drug-metabolizing organs
What is the effect of a high plasma concentration on the rate of elimination?
What is the effect of a high plasma concentration on the rate of elimination?
What is the equation for calculating total clearance?
What is the equation for calculating total clearance?
Which organ is the major contributor to drug excretion?
Which organ is the major contributor to drug excretion?
What is the formula to calculate Clearance (CL)?
What is the formula to calculate Clearance (CL)?
What is the purpose of determining the Elimination Half-life (t1/2) of a drug?
What is the purpose of determining the Elimination Half-life (t1/2) of a drug?
How does an increase in Volume of distribution (Vd) affect the Elimination Half-life (t1/2) of a drug?
How does an increase in Volume of distribution (Vd) affect the Elimination Half-life (t1/2) of a drug?
What is the effect of Renal failure on the Elimination Half-life (t1/2) of a drug?
What is the effect of Renal failure on the Elimination Half-life (t1/2) of a drug?
How does an increase in Clearance (CL) affect the Elimination Half-life (t1/2) of a drug?
How does an increase in Clearance (CL) affect the Elimination Half-life (t1/2) of a drug?
What is the effect of CYP450 induction on the Elimination Half-life (t1/2) of a drug?
What is the effect of CYP450 induction on the Elimination Half-life (t1/2) of a drug?
What is the renal clearance of a drug calculated as?
What is the renal clearance of a drug calculated as?
What is the glomerular filtration rate (GFR) measured as?
What is the glomerular filtration rate (GFR) measured as?
Why is creatinine used to measure glomerular filtration rate (GFR)?
Why is creatinine used to measure glomerular filtration rate (GFR)?
What does a high hepatic extraction ratio indicate?
What does a high hepatic extraction ratio indicate?
What is the hepatic extraction ratio calculated as?
What is the hepatic extraction ratio calculated as?
What does a renal clearance higher than creatinine clearance indicate about a drug?
What does a renal clearance higher than creatinine clearance indicate about a drug?
Study Notes
Clearance (CL)
- Defined as the volume of plasma cleared from the drug per unit time (L/hr or ml/min)
- Total body clearance (CL total) is the sum of all clearances from drug-metabolizing and drug-eliminating organs
- Kidney is the major organ of excretion, liver also contributes to drug clearance through metabolism and/or excretion into the bile
Factors Affecting Clearance
- Clearance depends on plasma concentration: high concentration → high rate of elimination, low concentration → low rate of elimination
- Clearance equation: CL = Q × (Ci – Co)
Elimination Half-life (t1/2)
- Time required for plasma concentration of a drug to decrease by 50%
- Depends on Vd and CL: t1/2 α Vd, t1/2 α 1/CL
- Used to determine duration of action and frequency of dosing
Factors Affecting Half-life
- Volume of distribution (Vd): ↑Vd → ↑t1/2, ↓Vd → ↓t1/2
- Clearance (CL): ↑CL → ↓t1/2, ↓CL → ↑t1/2
- Aging: ↓Vd → ↓t1/2
- Obesity: ↑Vd → ↑t1/2
- Pathologic fluids: ↑Vd → ↑t1/2
- CYP450 induction: ↓t1/2
- CYP450 inhibition: ↑t1/2
- Cardiac failure: ↓tissue perfusion → ↓clearance → ↑t1/2
- Hepatic failure: ↓clearance → ↑t1/2
- Renal failure: ↓clearance → ↑t1/2
Renal Clearance
- Renal excretion rate divided by plasma drug concentration
- Calculated using glomerular filtration rate (GFR) which can be measured using creatinine clearance rate (CrCl)
Extraction Ratio
- Removal of a drug by an organ specified as the extraction ratio
- Hepatic extraction ratio: fraction or percentage of the drug removed from the perfusing blood during its passage through the liver
- Drugs with high hepatic extraction ratio: large first-pass effect, low oral bioavailability
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Description
This quiz covers the concept of clearance in pharmacology, including total body clearance, its calculation, and the role of organs like the kidney and liver in drug clearance.
